1. Field of the Invention
The present invention generally relates to a power transmission mechanism for a power-driven tool.
2. The Prior Arts
A transmission mechanism of a conventional power-driven tool that is usually used for drilling or screw driving etc. can transmit the mechanical power from a motor to an output shaft via a gear system at various speed.
Referring to FIG. 4, the transmission mechanism of the conventional power-driven tool comprises a motor 1, a first planetary gear set 2, a second planetary gear set 3, a clutch 31, a connecting bar R, an intermediate shaft 5 and an output shaft 6, wherein the first planetary gear set 2 includes a first planet carrier 25 with a plurality of first planet gear shafts 251 extending therefrom and a plurality of first planet gears 23 respectively pivotally arranged on the first planet gear shafts 251, and a drive gear shaft 11 connected to the motor 1 is meshed with the first planetary gears 23. The first planet carrier 25 further has a clutch shaft 252 that is connected with the clutch 31. In addition, a circumferential groove 312 is formed on a rim of the clutch 31 for engaging with a switch (not shown) so that the clutch 31 moves with the switch. Furthermore, the second planetary gear set 3 includes a second planet carrier 35 and a plurality of second planet gears 34 pivotally connected to the second planet carrier 35, and the clutch 31 has two sun gears G1 and G2 connected thereto, wherein the first sun gear G1 is engaged with each second planet gears 34 and an internal gear 352 is formed on the second planet carrier 35 for meshing with the second sun gear G2. An end of the sun gear shaft having the first sun gear G1 and the second sun gear G2 arranged thereon is connected to an end of the intermediate shaft 5. The intermediate shaft 5 has a polygonal hole 5A. The connecting bar R is passed through the sun gear shaft and intermediate shaft 5, and has polygonal block R1 formed at one end thereof. An end of the output shaft 6 has a polygonal hole 61 corresponding to the polygonal block R1.
When the clutch 31 is axially moved to the first position (as shown in FIG. 4), the first sun gear G1 can be meshed with the second planet gear 34 and the polygonal block R1 received in the polygonal hole 5A of the intermediate shaft 5 is fitted into the polygonal hole 61 of the output shaft 6. Therefore, when the motor 1 drives the drive gear shaft 11 to rotate the first planetary gear set 2, the clutch shafts 252 of the first planetary gear set 2 drive the clutch 31 and the first sun gear G1 to rotate, the first sun gear G1 drives the second planetary gear set 3 to rotate, and then the second planet carrier 35 drives the intermediate shaft 5 and the output shaft 6 to rotate at low speed.
When the clutch 31 is axially moved to the second position (as shown in FIG. 5), the first sun gear G1 is disengaged from the second planet gear 34, the second sun gear G2 is engaged with the internal gear 352 of the second planet carrier 35, and the polygonal block R1 is disengaged from the polygonal hole 61 of the output shaft 6. When the motor 1 drives the drive gear shaft 11 to rotate the first planetary gear set 2, the clutch shafts 252 bring the clutch 31 and the second sun gear G2 to rotate, the second sun gear G2 brings the second planet carrier 35 to rotate, the second planet carrier 35 brings the intermediate shaft 5 to rotate at high speed and finally, the intermediate shaft 5 brings a part connected thereto to output the power.